The present invention relates to a system for deactivating a firing device for an airbag installed in a vehicle, circuit means being provided which prevent a current flow through the firing device during a desired deactivation time.
In the past, there have been a number of cases in which children who were sitting on the front passenger seat of the vehicle in a child seat directed backwards have suffered fatal injuries due to the triggering of the passenger-side airbag. These accidents could have been prevented by deactivating the passenger-side airbag. In general, there are situations in which activation of the passenger-side airbag is superfluous, for example, when the front passenger seat is not occupied by a person at all, but rather some object such as a piece of luggage is placed on it. There are systems and devices already known, which are mentioned in German Patent No. 197 24 344 C1, for detecting such situations in which the passenger-side airbag should be deactivated. Image-processing systems, which can detect whether the front passenger seat is occupied by a child seat or a person or an object and what distance the person is from the passenger-side airbag so that in critical occupancy situations the airbag can be deactivated, are very costly. Another device for detecting seat occupancy is composed of a mat, integrated into the front passenger seat, which changes its electrical resistance or its capacitance as a function of a force or pressure influence. Thus, this mat has the function of a weight sensor to determine whether the seat is occupied by a grown person or a child.
Furthermore, there are sensors which detect the presence of a backward-facing child seat on the front passenger seat. Among these are sensors which are based on an electromagnetic transponder principle, transmitters and receivers being disposed on the child seat and in the front passenger seat. European Patent No. 06 037 33 B1 describes an arresting device, also known under the name ISOFIX, for a child seat on the front passenger seat of a vehicle. The child seat is located in position by detent elements, present on the child seat, which can engage with a fixing device on the front passenger seat. A sensor detects the engagement of the detent elements and, in so doing, emits a pulse which is supplied to a control unit for deactivating the passenger-side airbag.
The simplest device for deactivating a passenger-side airbag is a manually operable switch which, as is derived from German Patent No. 197 24 344 C1 and U.S. Pat. No. 5,544,914, has a first switching position for activating and a second switching position for deactivating the firing device of the airbag.
All these indicated systems function such that they interrupt the electric circuit of the firing device to deactivate the passenger-side airbag. However, there have also been situations in which the passenger-side airbag has been triggered, even though it has been deactivated by software-programmed interruption of the firing circuit. Causes to be considered are possible malfunctions of a microcontroller in the airbag control unit, or even a direct irradiation of sufficiently great electromagnetic energy from outside into the supply lines of the firing devices. In the same way, short circuits to plus and minus of the battery voltage due to vehicle-body deformations caused by impacts could be responsible for triggering the airbag.
Therefore, an object of the present invention is to provide a system of the type indicated at the outset, which reliably ensures that under no circumstances can an unwanted triggering of the airbag occur.
According to the present invention, the firing device is bypassed with the aid of a switch, electrically controllable by the circuit means, which short-circuits the electric circuit of the firing device during the deactivation time. The result of this short-circuiting switch bypassing the firing device is that no current causing a triggering of the firing device, regardless of how this current is formed, can flow through the firing device.
Particularly to deactivate the passenger-side airbag when the front passenger seat is occupied in the ways mentioned at the outset, means are provided that signal such situations in which the firing device must not be triggered. For example, these means advantageously include a switch, operable by hand, or a sensory mechanism which detects the manner in which the seat is occupied. Or the means interact with a detent device with which a child seat is located in position on the front passenger seat of a vehicle, the means signaling a non-triggering case when the detent device is engaged.
Very great security against a false airbag triggering is ensured in that the circuit means keep the switch closed continuously, so that the firing device is short-circuited, and that the circuit means only open the switch when either a triggering or a diagnosis of the firing device is to be carried out.
For a diagnosis of the firing device, the switch is preferably opened at predefined time intervals for a duration of approximately 20 xcexcs. This time is less than the minimal firing lag time, which the firing device normally needs in response to a current flow, in order to trigger.
The electrically controllable switch is advantageously a field-effect transistor.
A first visual display can be provided which lights up in response to a short circuit of the electric circuit of the firing device, and a second display can be provided which lights up in response to a malfunction of the short-circuiting switch.